(163b) Pretreatment of RO Feed Water Via Filtration Aided By a Hydrocyclone Separation and Inline Coagulation

Pretreatment of reverse osmosis (RO) feed water is critical for avoidance of membrane fouling. In particular, removal of suspended matter, even at the sub-micron and nano size range is crucial to (i) avoid membrane fouling, and (ii) prevent heterogenous nucleation of mineral salts onto such particles (if present) at high recovery desalination of inland water of high mineral scaling potential. Accordingly, the present study presents an investigation of a pretreatment train that integrates a hydrocyclone with inline coagulant dosing, followed by microfiltration (MF) and ultrafiltration. Through optimization of coagulant selection and inline dose optimization, it is shown that a significant portion of suspended matter can be removed as flocs in the hydrocyclone separation unit. The effectiveness of the pretreatment train was evaluated using field groundwater and municipal title 22 treated water (prior to RO treatment). Initial coagulant selection, dose optimization, and evaluation of sequential dosing of different coagulants were based on jar tests. Inline coagulation tests with hydrocyclone revealed that, with inline coagulation residence time of ~15 seconds, a significant fraction of the source water total suspended solids (TSS) was removed, thereby lowering the burden on the downstream filtration units (MF and UF) for further TSS removal. Co-dosing with polyacrylamide and ferric chloride significantly enhanced flocculation and TSS mass removal above 60%. Moreover, microfiltration (1-2 µm) of the hydrocyclone treated water produced a filtrate turbidity <<0.1 NTU which is suitable for subsequent RO desalination step. The study demonstrated that inline coagulation with co-dosing and hydrocyclone treatment is effective for subsequent microfiltration to produce high quality feedwater for RO desalination. The treatment train presented in the present work is scalable and has the potential for enhancing operation efficiency and longevity of RO elements.